Lower Pilarcitos Creek Groundwater Basin Study - Coastside ...

Table of Contents
Page
Executive Summary ..........................................................................................................1
Background and Purpose...........................................................................................................................1
Scope and Study Area ...............................................................................................................................1
Acknowledgements ....................................................................................................................................2
Hydrogeologic Setting.......................................................................................................3
Location......................................................................................................................................................3
Climate .......................................................................................................................................................3
Land Use....................................................................................................................................................4
Groundwater Development and Wells........................................................................................................7
Soils ...........................................................................................................................................................9
Streamflow ...............................................................................................................................................10
Geologic Setting.......................................................................................................................................11
Hydrogeologic Cross Sections .................................................................................................................13
Lower Pilarcitos Creek Test Well Analysis......................................................................16
Drilling and Construction ..........................................................................................................................16
Hydraulic Analysis....................................................................................................................................18
Well Construction Program ......................................................................................................................21
Wellfield Operation and Life Expectancy..................................................................................................22
Marine Terrace Hydraulic Properties ..............................................................................24
Pumping Tests .........................................................................................................................................24
Groundwater Elevation Maps ...................................................................................................................25
Groundwater Fluctuations ........................................................................................................................26
Aquifer Storage and Usable Storage........................................................................................................27
Groundwater Discharge ...........................................................................................................................27
Saltwater Intrusion....................................................................................................................................27
Land Subsidence .....................................................................................................................................28
Watershed Water Balance ..............................................................................................30
Methodology and Data .............................................................................................................................30
Area above the Purisima Creek Gauge....................................................................................................31
Area above the Pilarcitos Creek below Stone Dam Gauge ......................................................................32
Area above Pilarcitos Creek at Half Moon Bay Gauge.............................................................................33
Groundwater Basin Water Balance.................................................................................35
Inflows ......................................................................................................................................................35
Outflows ...................................................................................................................................................40
Change in Storage ...................................................................................................................................42
Water Balance Equation...........................................................................................................................43
Drought Conditions...................................................................................................................................44
Trends ......................................................................................................................................................45
Previous Work..........................................................................................................................................46
Perennial (Safe) Yield ..............................................................................................................................47
Water Quality ..................................................................................................................50
CCWD Test Wells and Drought Relief Wells............................................................................................50
Groundwater Quality in AP Book 56 Area ................................................................................................52
Possible Anthropogenic Contamination Sources .....................................................................................52
Economic Feasibility .......................................................................................................54
Background ..............................................................................................................................................54
Water Quality and Treatment ...................................................................................................................55
Economic Feasibility.................................................................................................................................57
Conclusions.....................................................................................................................62
References......................................................................................................................63
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